(a) Field of the Invention
The present invention relates to a vehicle assembly line control system and method used for the production of vehicles.
(b) Description of the Related Art
The assembly of vehicles is generally realized through a plurality of main assembly processes--a vehicle body assembly process, a paint process, and a trim process--and the supply of parts for the main assembly processes. Parts supplied include basic parts such as the engine and transmission, and parts chosen as options by the consumer such as the stereo system, type of seats, etc.
In such a vehicle assembly process, it is ideal to sequence the vehicles to be assembled in a fixed pattern (for the vehicle body and trim processes) or consecutively (for the paint process). That is, production efficiency can be greatly increased in the vehicle body and trim processes if the vehicles are sequenced to be fed through the assembly process in an alternating pattern. For example, if the vehicles are arranged in an alternating pattern of type A and B vehicles, where type A vehicles require the mounting of automatic transmissions and type B vehicles require manual transmissions, both automatic and manual transmission assembly stations can operate simultaneously as the vehicles pass through the assembly line. However, if the vehicles are arranged in an A, A, A, B, B . . . pattern, the automatic transmission assembly station will initially be overburdened while the manual transmission assembly station remains idle, then vice versa as the B-type vehicles are fed through the assembly line. This sequencing of vehicles in a balanced manner for the assembly process is generally termed leveling.
On the other hand, vehicles requiring the same paint color and/or design should be grouped together and arranged sequentially for the paint process. This minimizes the number of times paint nozzles for the normally fully-automated paint process require cleaning. As a result, the time-consuming and costly process of cleaning the paint nozzles is reduced.
However, in such a prior art vehicle assembly line system, sequencing the vehicles for the three main vehicle assembly processes so that they are arranged to improve production efficiency often runs counter to one another. Namely, arranging the vehicles in an order that maximizes production efficiency for the vehicle body assembly process is normally inefficient for the paint process, and a sequence that is ideal for the paint process is not suitable for the trim process. For example, if the vehicles are arranged so that vehicles requiring the same paint color and/or design pass through the assembly line in sequence, production efficiency for the vehicle body assembly process and trim process is drastically reduced.
Various prior art vehicle assembly systems and methods have been developed to solve such problems. Referring to FIGS. 9 and 10, shown respectively are a flow chart of a prior art vehicle assembly method and a schematic diagram of a prior art vehicle assembly system using the method described in FIG. 9.
In the prior art vehicle assembly method, a host computer system first receives vehicle production orders via a business and sales network in step S1. Next, in step S2, a daily production plan is established according to the production orders and transmitted to a production planning system. According to the daily production plan, a main computer of the production system then places orders for required materials and parts in step S3.
Following the above step and using the daily production plan as a basis, a vehicle body production plan is established in step S4, a vehicle body assembly sequence is arranged in step S5, and vehicle bodies are assembled through metal pressing, welding, and other processes in step S6. In the vehicle body assembly sequencing step S5, leveling is performed to increase production efficiency. Also, during the assembly of the vehicle bodies in step S6, vehicles found having defects are temporarily removed from the assembly line, corrected, then replaced back into the assembly line.
Next, completed vehicle bodies are temporarily placed in a white body storage (WBS) in step S7. In the WBS, the completed vehicle bodies are re-sequenced in an order ideal for the paint process. That is, the vehicle bodies are grouped together such that those requiring the same paint color and/or design are fed through the paint process following one another consecutively.
In the paint process, the vehicle bodies first undergo waterproofing and undercoating processes, after which they are painted in the colors and/or designs according to the production plan. For the painting of vehicles, it is now standard practice to utilize robotic technology for the paint process. Because of the high cost of such machinery, most vehicle assembly lines normally utilize only a single robotic system. As a result, the paint nozzles must be cleaned before the introduction of each new paint color. Accordingly, the vehicle bodies undergo a color grouping process in the WBS or during the paint process as described above such that a group of consecutive vehicle bodies can be painted to minimize the number of times the paint nozzles require cleaning. Further, in the paint process, as in the vehicle body assembly process of step S6, vehicles found to have defects are removed from the assembly line, corrected, then replaced back into the assembly process.
After the paint process of step S8, the vehicles are placed in a painted body storage (PBS). In the PBS, the vehicle bodies are again re-sequenced so that they are placed in an ideal sequence for the trim process in step S9.
Next, parts chosen as options by the consumer and other various final parts are mounted to the vehicle bodies to complete the trim process in step S10, thereby concluding the vehicle assembly process.
However, in the above prior art vehicle assembly method, much time is required to fully rearrange the vehicles in the WBS and PBS to an ideal sequence for the subsequent processes. For example, when the vehicles are placed in the WBS after the vehicle body assembly process, the re-sequencing of the vehicle bodies so that they are clustered together in groups requiring the same paint color and/or design for the paint process is time consuming. Accordingly, production efficiency is greatly reduced.
This problem is compounded by two factors: 1) the sequencing of the vehicles for the vehicle body assembly process prior to assembly, for the paint process in the WBS, and for the trim process in the PBS is done to meet ideal conditions for that process only without consideration to the subsequent process, and 2) the removal of defective vehicle bodies for correction of the same in the vehicle body and paint processes additionally complicates the sequencing.
Further, when vehicles are removed from the assembly line during the vehicle body assembly process and paint process as a result of discovered defects, if the defect is not quickly corrected and the vehicle body replaced, or if the defective vehicle is the last in the grouping (e.g., of a particular paint color), the advantages of sequencing the vehicles can not be realized. This problem can become severe if defects are found in a number of consecutive vehicles.
Finally, because it is not practical to provide enough physical space for the WBS and PBS to fully perform their function (i.e., to hold enough vehicle bodies to perform their task of re-sequencing the same), there is a limit to how much the vehicle bodies can be rearranged for the subsequent steps. Accordingly, vehicles are often assembled more slowly than the established production plans.